PSA: Why small hub motors overheat and fail

ESK8 Electronics
161

Can rolling drag be a reason for this huge difference?

In riding condition drag is almost not noticed with hubs because there is lot of weight over a single rotation axe, no peripheral loads, magnets drag becomes negligible compared to the rider’s weight.

What about unloaded free spinning, magnets drag should become a more important data to account for thus require more amps (usually lost in the mass of wasted amps necessary to haul some weight around).

Or that’s my misunderstanding and it is all about copper resistance : more copper cable length to feed = more energy wasted?

162

Your talking about belts drives. Belt drives have resistance when spinning without a load. Add more belt drive motors, and you gain more resistance, so yes, it takes more energy.

Good hub motors have little to no resistance when spinning without power. Add more, and you split up current and you should reduce waste. I’m not 100% sure, since I haven’t done real world tests. But @FredSaberhagen has a good point.

If you ride in variable terrain like me, then theres times I need to climb mountains, and theres times I need to ride flat for miles, in the same trip. Now you’ll say a dual drive belt system can be geared to be efficient for both circumstances, I see that one coming.

Hub motors are a bit different. When climbing steep hills, due to the disadvantage I believe we all agree on now thanks to frank. 4wd gives good efficiency at all times. Why is it that I could get 20 miles with a 4wd hub motor and 8ah battery (if in the ideal conditions), and little heat, if it was not efficient?

Even if I was to get worse efficiency with 4, I get closer to the no load speed, more predictable acceleration, better handling (especially around corners), and your doing less work per motor, so you should expect a better life cycle.

Yes, it costs more up front, but if it last 5 years instead of 3, is it really that much more?

The only real downside is more weight. But for people like me, it’s not an issue. I hope on and go to class. Put it down, charge it, and when I’m ready to go home, I unplug and go. I don’t need to carry it around very much.

Even if it is less efficient, by how much? Clearly, not what your saying. I don’t think anyone can get 40 miles on an 8ah 12s battery. If for some reason, it’s not as efficient. At most, I would expect 25 miles from a good belt drive setup with this battery. That 5 mile difference is more likely a result of rider weight in this case, rather than efficiencies.

163

No, I am talking about a motor unattached and spinning free at WOT. I don’t know how I could have made that more clear.

164

You said it sounds like 4 should better in theory, but not in the real world. Putting them on a board and riding is real world. Spinning them on the bench is not real world. The currents are low, and don’t simulate what happens when they are ridden.

165

@evoheyax What I get from this, is there is no way the motors will draw less when placed on the ground and weighted…And when Chaka say’s unattached, he means no wheels or belts, which is as direct a comparison to hubs as we can get.

166

Well can you explain my real world range numbers?

Cause I’m not really behind belt drives in range anymore…

If it really used more power, how come I’m not seeing this in the real world?

167

All the inefficiencies in a motor can be categorized. Running MOTors wot the current draw reveals the iron losses. A bigger motor has more and less copper losses. A bigger motor will therefore generate heat more from high rpm than load. Only other losses are air friction and bearings. The thought that more small MOTors will have more iron losses than one big motor…I doubt it but still greater losses and higher no-load would likely happen from the increase in bearings and their friction. Less thick grease in bearings would bring it down Actually the iron losses can go up when stators are magnetically saturated with a very large load and then they don’t switch polarity as easily. But otherwise they stay the same and are just rpm dependent

168

Using your figures it looks like you are using about 17 watthours per mile. This is what I would call moderate to heavy usage and is what we see in a belt drive belt for moderate speeds around 30-40 mph. My board is geared to hit the low 40’s and I use close to 20 watthours per mile but this is with “full throttle all the time” riding on highways. The high usage is due to the tall gearing in those drives. We see much better numbers from single drives with lots of reduction, geared to max out around 22-25 mph.

169

Well now we’re comparing apples to oranges again…

If I wind a hub to 20 mph top speed, yea I’ll be better off than having hubs with a max speed of 30 mph.

I will give you real world numbers when I ride home later today of what my actual WH per mile is. it used to be 7 wh per motor, so 28 wh total. Given, that’s harsh riding in a hilly environment with a 200 lb guy. I expect the numbers will be around 4 wh per mile now per motor, or 16 ish total. If I were to be really kind, I bet I could get that a bit lower.

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170

I used @Ackmaniac 's app and left my board on for several weeks to get my average usage. Best to get a large data set when we talk about these numbers. You should go ahead and wind a motor to max out at 22-25mph and see what happens, get back to us when you do. Not enough results from testing hubs can be found so keep it coming!

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171

@evoheyax so somehow adding more holes to the bucket gives us fewer leaks?

I have built no less than 5 distinct all wheel drive boards and i have to say that by the time the tweaking is done to allow the use of four power plants on the same pack i had two on, not even the brakes improve that much. Acceleration does not improve. I’m still throwing the same watts on the street, but now throwing more current back into the pack while braking, making it an even more precarious balance of settings.

In order to take advantage of the full power of four wheel drive over a two wheel drive you need twice the cells and twice the power bandwidth in the copper, and twice the BMS.

172

Yes, the leaks are all smaller right? Am I right?! Am I right?! In your Face!!!

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173

i’m going to go home tonight and dedicate myself to science by seeing if more beers results in less piss.

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174

12 beers one person? Or 12 beers 4 people?

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175

Leaks= winding resistance. Adding MOTors that are all .06ohms, they aren’t in series or parallel but separate circuits. U still have .06ohm resistance regardless of how many motors. More so the advantage w multiple motors I think would be how current creates heat w a square relationship …and now all MOTors have a forth of that current. That’s what I think this hour .

176

See, it doesn’t even hold up here. I person can more efficiently pass more beer through one body resulting in more piss than four clones could due to losses from pirspiration and metabolic inefficiencies.

To be clear, i’m saying if i drank 12 beers i would piss more than if four of me each drank 3.

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177

and then you have mechanical resistance. on belts its more, but on hubs you still have bearings, even though by comparison its almost none. That gets multiplied by four as well.

178

Were any of these boards hub motor boards first of all?

Second of all, what your saying makes no sense.

If I have 2x 4.12 vescs, I’m limited to 260 motor amps, due to the 4.12 vescs’ 130 amp limit.

Now, if I have 4x 4.12 vescs, I’m limited to 520 motor amps, double to power potential.

Now, you might not be hitting that limit with 2wd and belts, so for you, this is a non issue.

But I’m telling you, If I turn 2 of my vesc’s off right now, I will not get as good of an acceleration or braking. I simply can do more than what the limits of the controllers are.

Now with the focbox and vesc 6, you might hit this bottle neck and thus, not have as much of an issue. You probably can beat a 4wd with a single, huge belt drive motor. But man, good luck controlling that jerk of having one motor accelerate like that. With the motors most are using, the jerk is minimal, but if you want to match the power 4 of these hubs have, your going to need a huge motor for your belt drive. These also better control.

Maybe we just have to realize that at the end of the day, hubs and belts are just different systems. Maybe 4wd with belts are not going to give you much benefit (besides you’ll get closer to the no load speed), but with hubs, more motors = more torque.

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179

12/4=3 beers, I won’t even break the seal… is that 100% efficiency?

If I drink three beers while riding my board will I go further? all this beer talk is making me thirsty

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180

I don’t think beers is a good analogy as the piss produced is equal to beers drank but if u drank …something that expanded based on its total volume similarly to how the main copper losses in the motor occur, and that liquid were to expand w a square relationship…then the four clones drinking a beer each would piss two beers each but if u drank all four beers ud piss like 16 beers. If they all drank 2 beers then they’d piss 16 beers worth of liquid and if u drank all 8 beers ud piss 56 beers worth

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